linux-kernel - Re: [PATCH 24/25] perf tools: Add multi file '-M' option for record command

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Date:	Mon, 2 Sep 2013 11:40:02 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	David Ahern <dsahern@...il.com>
Subject: Re: [PATCH 24/25] perf tools: Add multi file '-M' option for record
 command

On Mon, Sep 02, 2013 at 12:11:35PM +0300, Adrian Hunter wrote:
> On 02/09/13 11:37, Jiri Olsa wrote:
> > On Mon, Sep 02, 2013 at 10:52:46AM +0300, Adrian Hunter wrote:
> >> On 01/09/13 13:36, Jiri Olsa wrote:
> >>> split event data into multiple files based on the file
> >>> size or time delta specified as an argument to the option.
> >>>
> >>> Adding multi file '-M' option for record command to store
> >>> output perf.data into multiple files based on the size
> >>> threshold.
> >>>
> >>> The threshold is specified either as size (B/K/M/G) or time
> >>> (s/m/h) by appending the size with appropriate unit, like:
> >>>   -M 5M for 5 megabytes threshold
> >>>   -M 1h for 1 hour threshold
> >>> The generated name for each data file is appended with sequential
> >>> number (prepended by 5 zeros).For default output file name it
> >>> will be:
> >>>   perf.data-00000
> >>>   perf.data-00001
> >>>   perf.data-00002
> >>>   ...
> >>>
> >>> Also watermark/wakeup_watermark is set accordingly to get
> >>> wake ups more often so we could get close enough to the
> >>> file size promise.
> >>>
> >>> Example:
> >>>   $ perf record -M 5M yes > /dev/null
> >>>   ^C[ perf record: Woken up 228 times to write data ]
> >>>   [ perf record: Captured and wrote 20.246 MB perf.data-[0-4](~884542 samples) ]
> >>>   yes: Interrupt
> >>>   $ ls -l perf.data-0*
> >>>   -rw------- 1 jolsa jolsa 5289856 Aug 16 16:07 perf.data-00000
> >>>   -rw------- 1 jolsa jolsa 5296008 Aug 16 16:08 perf.data-00001
> >>>   -rw------- 1 jolsa jolsa 5344968 Aug 16 16:09 perf.data-00002
> >>>   -rw------- 1 jolsa jolsa 5309144 Aug 16 16:09 perf.data-00003
> >>>   -rw------- 1 jolsa jolsa 2358268 Aug 16 16:09 perf.data-00004
> >>
> >> Did you consider doing this with "perf inject" instead of "perf record"?
> >> That way you could get the split exactly right, and you could split the same
> >> file different ways.
> > 
> > right, this could be added into inject command as well
> 
> I was really thinking "instead" not "as well" e.g.
> 
> 	perf record yes | perf inject -M 5M
> 

yep, got it.. this gives you more fine grained size resolution
and lets you split already stored data files, nice

But while I think this is nice feature to have, two things keeps
me thinking we should leave the support in record command as well:
  - the extra inject command overhead, that needs to parse the whole
    stream, which might not be wanted in some cases
  - AFAIU the vast majority of perf users do just record/report
    and would be restrained from this feature ;-)

jirka
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